The best is hands down, easily, no questions asked the gt40. Although the panoz has the exact same sound, so it's hard not to say it's equal.
Some of those cars on that list make me laugh: the zonda is inaudible, the cobra sounds nothing like the beast that it should, the opel calibra should be there, not the astra.
Overall, a lot of the tones are pretty good, but they are just too damned quiet. I mean if you put racing exhaust on any car it will be loud as hell. Especially, a 700 horsepower v8.